Moving a rudder outboard

[frank smith]

I have been looking at a design with an under hung rudder , and think it might make some sense to move it to the transom .
If one was going to move an under hung rudder to the transom , what other changes would you have to make ?
FS

[urisvan]

you need to add some fittings(hinge) to transom, to connect the rudder to the transom.

[PAR]

The gudgeons will take surprisingly high loads, so through bolt if possible. From a design stand point you'll lose a little efficiency, compared to the under hung.

[frank smith]

Originally Posted by PAR

The gudgeons will take surprisingly high loads, so through bolt if possible. From a design stand point you'll lose a little efficiency, compared to the under hung.

The reason for the change is put the ruder assembly where it can be gotten at , as well as adding a trim tab . I assume the Coe will move aft , and the lead will with it .What handling changes can be expected . I know there is a history of this kind of change on boats with short keel where the rudder was hung on the keel .

[PAR]

The CE will not move anywhere. The CLP might move a touch and the lead will increase, but not likely enough to worry about on most modern hull forms. At this point it would be handy to know what design you're contemplating this change on. If it has a full length keel, like the old CCA's boats, then you may notice some balance differences, but again knowing what we're working with will be helpful.

[urisvan]

hi PAR,
i agree that the efficiency of the rudder will decrease because of the free surface effect. But;
Doesn't it improve the handling capabilities a little bit, as the leverage to steer the boat will increase

regards
ulas

[gonzo]

In rough weather the rudder may ventilate and/or come out of the water with loss of control. It is impossible to give a good answer without looking at the design.